Problem 68 - Calculate With Confidence

Question

Round weights and dosages to the nearest tenth as indicated. Order: Amprenavir \(650 \mathrm{mg}\) p.o. t.i.d. for a child weighing \(66 \mathrm{lb}\). The recommended dosage is \(22.5 \mathrm{mg} / \mathrm{kg}\) up to three times a day. Is the dosage ordered safe?

Step-by-Step Solution

Answer

Yes, the dosage of 650 mg is safe for the child.

Step 1: Convert Pounds to Kilograms

The first step is to convert the child's weight from pounds to kilograms. Use the conversion factor: 1 lb = 0.453592 kg.Calculate:\[ 66 \text{ lb} \times 0.453592 \text{ kg/lb} = 29.937072 \text{ kg} \]Round this to the nearest tenth:\[ 29.937072 \approx 29.9 \text{ kg} \]

Step 2: Calculate Maximum Safe Dosage Per Dose

Next, calculate the maximum safe dosage per dose using the recommended dosage of 22.5 mg/kg.Calculate:\[ 22.5 \text{ mg/kg} \times 29.9 \text{ kg} = 673.75 \text{ mg} \]The nearest tenth gives us:\[ 673.75 \approx 673.8 \text{ mg} \]

Step 3: Evaluate Ordered Dose

Now, compare the ordered dosage of 650 mg with the calculated maximum safe dose of 673.8 mg per dose. Since 650 mg is less than 673.8 mg, the ordered dosage is within the safe range.

Key Concepts

Weight Conversion

In pediatric dosage calculations, converting a child's weight from pounds to kilograms is fundamental. Understanding the conversion is critical because most medication dosages are prescribed based on the child's weight in kilograms. To convert weight, use the simple conversion factor where 1 pound (lb) is equal to 0.453592 kilograms (kg). Multiply the child's weight in pounds by this factor to find the weight in kilograms.
For example, if a child weighs 66 pounds, the calculation will be:

• Calculate: \(66 \text{ lb} \times 0.453592 \text{ kg/lb} = 29.937072 \text{ kg} \)
• Round to the nearest tenth: \(29.937072 \approx 29.9 \text{ kg} \)

Ensure to round the calculated weight to the nearest tenth for precision in dosing. This accurate weight in kilograms is essential for safe and effective medication administration.

Safe Dosage Limits

Understanding safe dosage limits is crucial when administering medications, especially in pediatrics. Safe dosage limits determine the maximum amount of a drug that can be safely given to a child, reducing the risk of overdose. This limit often varies based on the weight of the child and the specific medication.
To calculate, use the recommended dosage (usually specified in mg/kg) and multiply it by the child's weight in kilograms. For instance, if the recommended dosage is 22.5 mg/kg and the child's weight is 29.9 kg:

• Calculate: \(22.5 \text{ mg/kg} \times 29.9 \text{ kg} = 673.75 \text{ mg} \)
• Round to the nearest tenth: \(673.75 \approx 673.8 \text{ mg} \)

This calculated result represents the maximum safe dose per administration. Always ensure that the prescribed dose does not exceed this limit to maintain patient safety.

Drug Administration Calculations

Drug administration calculations involve comparing the ordered dose with the calculated safe dosage to ensure its safety. Once you have converted the weight and calculated the safe dosage, the next step is to verify that the prescribed medication dosage is safe and appropriate.
Consider the ordered dose against the safe maximum calculated. For example, if the ordered dose is 650 mg and the calculated safe maximum is 673.8 mg, compare these values:

• Ordered dose: 650 mg
• Safe maximum dose: 673.8 mg

Since the ordered dose (650 mg) is less than the maximum safe dose (673.8 mg), it falls within the safe range. Always perform this check before administering any medication to prevent the risk of overdose and ensure the safe treatment of the child.